Background/Objectives: This study sought to identify key barriers to treatment adherence in children and adolescents with type 1 diabetes (T1D) using the Adherence Starts with Knowledge-12 (ASK-12) questionnaire and to evaluate its impact on metabolic control, providing insights for optimizing T1D management. Methods: A total of 160 children and adolescents with T1D aged 5–18 years who sought treatment from a pediatric endocrinology outpatient clinic between June and August in 2022 were prospectively examined. The patients’ low treatment adherence (LTA) or high treatment adherence (HTA) was determined based on their ASK-12 questionnaire scores. Two pediatric endocrinologists reviewed the participants’ medical records and then classified them into two groups: tight metabolic control and poor metabolic control. Results: LTA, which was determined based on the participants’ ASK-12 scores, was significantly associated with puberty, presence of diabetic ketoacidosis, and daily self-management (p < 0.001, p < 0.001, and p < 0.001, respectively). Those whose ASK-12 scores indicated LTA were older and had a longer duration of T1D, higher hemoglobin A1c levels, and lower BMI-SDS values than those with HTA) (p < 0.001, p < 0.001, p < 0.001, and p < 0.001, respectively). A total of 94 (59%) participants were indicated to have HTA, but 24 (25.5%) of them were found by the clinicians to have poor metabolic control. Conclusions: The ASK-12 questionnaire scores can identify pediatric patients with T1D who exhibit LTA and thus may be beneficial for early recognition of low adherence. Approximately 25% of the patients with ASK-12 scores indicating HTA were at risk of poor metabolic control. Puberty, duration of T1D, BMI-SDS, HbA1C, and parental involvement alongside ASK-12 score may be considered to improve treatment compliance. Integrating these variables into adherence assessments may enhance treatment compliance and improve long-term outcomes in pediatric T1D management.